1. Field of the Invention
The present invention relates to a semiconductor laser module, and more particularly to a structure of a semiconductor laser module including a Peltier effect element installed in a metal casing.
2. Description of the Related Art
FIG. 4 is a sectional view showing a typical arrangement of a conventional semiconductor laser module having a Peltier effect element.
The semiconductor laser module, as shown in FIG. 4, includes a semiconductor laser 1, an optical system, and an optical fiber 3. The semiconductor laser 1 is mounted on a substrate 6 together with a monitoring photo-diode 4 and a first lens 5. The substrate 6 is fixedly mounted in a metal casing 8 through a Peltier effect element 7. The metal casing 8 has a window in its one side wall which is sealed with a hermetical glass plate 9, and a second lens 10 is fixed outside the side wall by a lens holder 11. More specifically, one end of the lens holder 11 holding the lens 10 is fixedly secured to the side wall in such a manner that the lens holder is coaxial with the window. A ferrule holder 12 is secured to the other end of the lens holder 11, and a ferrule 13 into which one end portion of the optical fiber 3 is fixedly inserted is inserted into the ferrule holder 12.
FIG. 5 is an enlarged diagram showing the Peltier effect element 7 and its relevant components in the semiconductor laser module shown in FIG. 4.
The Peltier effect element 7, as shown in FIG. 5, is formed of a pair of ceramic plates 71 and 72 which are arranged in parallel with each other with a certain space between them; and a plurality of thermoelectric elements 74 held through electrodes 73 between the ceramic plates 71 and 72. The Peltier effect element 7 is fixedly provided inside the metal case 8; more specifically it is fixedly mounted on the inner surface of the bottom wall of the metal casing 8 with SnPb solder 2.
The conventional semiconductor laser module thus constructed has a problem that the solder 2 fixing the Peltier effect element 7 may flow over to the upper surface of the ceramic plate 71 so as to short-circuit the electrodes on the ceramic plate 71.
It is an object of the present invention to provide a semiconductor laser module capable of installing a Peltier effect element more certainly.
The semiconductor laser module according to the present invention includes a metal casing of the semiconductor laser module, a semiconductor laser and a Peltier effect element mounted on the inner surface of the metal casing by soldering. In the semiconductor laser module of the present invention, the metal casing has a Peltier effect element mounting region in the inner surface of the metal casing on which the Peltier effect element is mounted, the area of the Peltier effect element mounting region being substantially equal to that of the bottom surface of the Peltier effect element, and the Peltier effect element mounting region being with respected to a region adjacent thereto.
In the semiconductor laser module according to the present invention, a step is formed around the Peltier effect element mounting region so that the Peltier effect element mounting region is higher than the surrounding area. This structure prevents excess solder from short-circuiting the electrodes of the Peltier effect element when mounted. That is, the excess solder is not permitted to rise over the upper surface of the ceramic plate of the Peltier effect element.